The present invention relates to a powertrain and a control method for the powertrain for a hybrid vehicle comprising two separate power sources, e.g. an internal combustion engine and an electric motor.
In hybrid vehicles with automatic or semi-automatic transmissions (automatic or automatic in manual mode) is it desired to provide an efficient powertrain and powertrain control in order to be able to use the propulsion units efficiently. For hybrid vehicles, it is common practice to connect both propulsion units, e.g. an internal combustion engine and an electric motor, to the same gear box or transmission. Different powertrain arrangements and methods for the control of hybrid vehicles are for example disclosed in US 2007/022 835, US 2011/030 488, US 2010/065 353, US 2008/234 098 and DE 101 43 289. By controlling the powertrain automatically, different control strategies may be used efficiently depending on the desired goal to achieve, e.g. fuel efficient or smooth driving of the vehicle. Even though the above described arrangements provide working examples of powertrains for hybrid vehicles, there is still a desire to provide improved powertrain arrangements for hybrid vehicles.
The present invention, according to an aspect thereof, is directed to a powertrain for a hybrid vehicle and a control method for such a powertrain. The configuration of the powertrain enables a control method for a hybrid vehicle which is able to avoid or reduce power interruptions in the powertrain when changing gears.
The powertrain according to an aspect of the invention comprises a first propulsion unit and a second propulsion unit for propulsion of the vehicle. These propulsion units are connected to a transmission having a double clutch arrangement, a so called Dual Clutch Transmission (DCT). The DCT comprises a first input shaft connected to the double clutch arrangement and this first input shaft is connected to the first propulsion unit, e.g. an internal combustion engine (ICE). The double clutch is arranged such that when the first clutch is engaged, the first input shaft of the DCT is mechanically connected to an output shaft via a first power path and when the second clutch is engaged, the first input shaft of the DCT is mechanically connected to the output shaft via a second power path. Each of these two power paths comprises a main gear box, the same main gear box may be used for both power paths or two separate main gear boxes may be used for the different power paths. The main gear box, or main gear boxes, used comprises at least two gears having different gear ratios. Hence, a torque provided by the first propulsion unit is transferred from the first input shaft of the DCT to the output shaft of the DCT via either of said first and second power paths. The first and second power path are designed such that they define an overall gear ratio from the first input shaft to the output shaft which may differ depending on which path that is used and the selected gears of the selected power transmitting power path. The overall gear ratio is thus defined by at least the ratio of the selected clutch and the ratio of the selected gear in the main gear box associated with the selected clutch. There may of course be further arrangements which influence the gear ratio, either additional fixed gear ratio transmissions in the power path or further shiftable gears in addition to the gears of the main gear box. The gear ratios of the first and second power path are generally arranged such that a one-step gear shift, upshift or downshift, of the overall gear ratio from the first input shaft to the output shaft involves a shift of the power path for at least some of the gears. This means a one-step gear shift involves a change of the engaged clutch of the double clutch arrangement. In general, the gear ratios for this kind of gear boxes having a double clutch are adapted such that consecutive gears are defined in different power paths such that a one-step gear shift always involves a change of the engaged clutch in the double clutch arrangement.
The second propulsion unit, e.g. an electric motor, is connected to the second power path via a second input shaft to the power train. This means that the second input shaft is connected to the second power path downstream of the double clutch arrangement, i.e. the double clutch arrangement is bypassed. Hence, the power from the second propulsion unit will thus be transferred to the output shaft via the second power path when connected to the power train via the second input shaft. The second input shaft is connected to the second power path upstream the main gear box associated with the second power path such that a shift of the main gear for the second power path always also causes a shift of the main gear ratio from the second input shaft, connected to the second propulsion unit, to the output shaft. The second propulsion unit may be connected to the second input shaft via a clutch and/or a fixed gear ratio change.
The power train and DCT are connected to an Electronic Control Unit (ECU) which is configured to control the engagement and disengagement of the first and second clutches of the double clutch arrangement. The ECU is also configured to control the gear positions of the gears of the main gear box, or main gear boxes, associated with each one of the first and second power paths. The ECU may also be programmed to control the propulsion units and/or further clutches or gears comprised in the power train. By ECU is meant in this context either a single processor or a multitude of processors and memories which together form the ECU.
The above described configuration enables certain positive benefits when changing a gear such that the power interruption during gear changes is avoided or decreased.
The ECU may thus be programmed to control the power train during a gear shift and control gears, clutches and propulsion units. According to a first aspect of the invention, the ECU may control the powertrain such that the mechanical connection between the second propulsion unit and the second power path is maintained when there is a gear shift desired for changing the overall gear shift ratio from the first input shaft to the output shaft which involves a change of the engagement of the second clutch of the double clutch arrangement to be disengaged and the first clutch of the double clutch arrangement to be engaged. Hence, the mechanical connection in the second power path from the second input shaft to the output shaft is maintained when there is a change of engagement from the second clutch of the double clutch arrangement to the first clutch of the double clutch arrangement. To maintain the connection means that the connected second propulsion unit may for example be used either for braking, in case there is a desire for a braking operation during the gear shift, or to provide a propulsion force in case it is desired to provide continued propulsion torque during gear shift. If the second propulsion unit is an electric motor/generator, the braking force may be used to generate electricity.
According to a second aspect of the invention the ECU may be programmed to control the gear shifts to reduce the power interruptions when there is gear shift of the overall gear ratio from the first input shaft to the output shaft including a change of the double clutch engagement from the first clutch, engaging the first power path, to the second clutch, engaging the second power path. In this case the power connection between the second propulsion unit and the second power path may be maintained provided that the desired gear of the main gear box associated with the second power path is already selected in order to shift to the desired overall gear ratio from the first input shaft to the output shaft. This may for example be the case when there has been a one-step upshift to an overall gear ratio which is transferred to driving wheels via the first power path and there is a subsequent desire to perform a one step down shift, back to the previously used overall gear. This example is valid provided that no gear shift has been made in the main gear box associated with the second power path in between the upshift and downshift and that the two consecutive gears are designed to be selected by changing the double clutch engagement between the first and second clutch of the double clutch arrangement.
According to a third aspect of the invention the ECU may be programmed to control the gear shifts in an efficient way when there is gear shift of the overall gear ratio from the first input shaft to the output shaft including a change of the double clutch engagement from the first clutch, engaging the first power path, to the second clutch, engaging the second power path when there also is a need for performing a shift in the main gear box associated with the second power path. When performing this gear shift, the ECU may be programmed to control the power train such that the power connection in the second power path between the second input shaft connected to the second propulsion unit and the output shaft is interrupted while said shift of the main gear in the second power path is performed. However, the shift of the main gear in the second power path is performed before the change of the double clutch engagement from the first clutch to the second clutch is performed. In this case there is thus maintained a power connection between the first propulsion unit and the output shaft via the first power path having the first clutch of the double clutch arrangement engaged while the shift of the main gear associated with the second power path is performed.
Hence, the design of the powertrain enables the ECU to be programmed to control the powertrain in an efficient way to reduce or avoid power interruptions as described above. To be noted, the control strategies of the ECU as described above according to the first, second and third aspects of the invention may be used together all three of them, only two of them (any two) or being used separately. Hence, the ECU may be programmed as desired in order to perform these desired control strategies.
The powertrain may as previously mentioned be designed such that there is a common main gear box used for the first and second power path. Since the same main gear box is used for both power paths, the possible gear ratios in the main gear box for the different power paths are thus the same. In order to get different gear ratios from the different power paths the double clutch arrangement may be designed such that the power path which transfers torque via engagement of the first clutch of the double clutch arrangement provides a power connection representing a first gear ratio and when the second clutch is connected to the gear box is the second connection representing a second gear ratio different from the first gear ratio.
In order to provide an efficient shift of gears, the first and second clutches of the double clutch arrangement may engage with the main gear box at different positions representing the different power paths such that a change of the gear in the main gear box for the power path which not is engaged may be shifted while transmitting torque via the other power path. For example may the first clutch be connected to a main shaft or gear wheels of the main shaft in a main gear box while the second clutch may be connected to always engage with a countershaft of the main gear box.
The double clutch may thus provide two different gear ratios of the input power before the power reaches the main gear box.
In the above described configuration, an Internal combustion Engine (ICE) may be the first propulsion unit connected to the first input shaft and an Electric Motor (EM) may be used as the second propulsion unit. The EM is preferably designed such that it may be used as a generator for generating electricity when used for braking. Hence, the ICE may in this case be connected to the double clutch arrangement and the EM to the countershaft. To connect the EM to the countershaft is in general a more space saving way to connect the second propulsion unit to the gear box than using the main shaft. However, the EM could be connected to the main shaft instead.
Above has been exemplified that a single main gear box is used for both power paths. The single gear box could easily be replaced for two main gearboxes if desired. In this case is it not necessary to provide different gear ratios for the first and second clutch of the double clutch to the input shaft of the gear boxes in order to provide different gear ratios for the different power paths since the gears of the two main gear boxes may be designed such that they provide different gear ratios. Furthermore, each gear box may be provided with separate input shafts. Gear shifting in said Dual Clutch Transmission (DCT) can be initiated manually by the driver according to known art or being automatically controlled.
In an embodiment of the invention, the power train may be exemplified by a system comprising a DCT having a double clutch arrangement having a high (H) and low (L) gear ratio and a single main gear box having 3 forward gears (M1, M2, M3) and a reverse gear (R). The gear ratios of the main gears in the main gear box and the gear ratio of the first and second clutch may be designed such that from the first input shaft to the output shaft there are 6 different forward gears and 2 reverse gears provided, the gear ratios of the first and second clutch and the forward gears of the main gear box designed such that every second gear is associated with the same power path, i.e. a power path enabled by engagement of the same clutch, such that a one-step gear shift of the overall gear ratio from the first power path to the second power path involves a shift of the engaged clutch in the double clutch arrangement for all forward gears.
The invention further relates to a control method for a power train comprising a first and second propulsion unit for powering the vehicle and a Dual Clutch Transmission (DCT). The DCT comprises a first input shaft and an output shaft wherein the first input shaft is mechanically connected to a double clutch. The double clutch arrangement comprises a first clutch defining a first power path and a second clutch defining a second power path from the first input shaft to the output shaft. Each power path comprises a main gear box having at least two gears having different gear ratios. The main gear box may be the same for both power paths or two separate main gear boxes. The first propulsion unit is mechanically connected to the first input shaft such that a torque provided by the first propulsion unit is transferred to the output shaft via either of said first and second power path depending on which of the clutches of the DCT that is engaged. Each of the power paths has gear ratios defined by the gears in the power path including the gear ratio of the respective clutch and the gears of the associated main gear box such that an overall gear ratio from the first input shaft to the output shaft is defined. By gear ratio of the respective clutch is meant a gear ratio which is connected to the power path of the clutch which is not common for both power paths, i.e. a gear ratio which is solely connected with and only dependent on the selected clutch of the double clutch. At least some of said gear ratios of the first and second power path are designed such that a one-step upshift or downshift of the overall gear ratio from the first input shaft to the output shaft involves a shift of the power path, i.e. a shift of the engaged clutch in the double clutch arrangement. The second propulsion unit is connected to a second input shaft which does not involve the double clutch arrangement. The second input shaft is connected to the second power path downstream the double clutch but upstream the associated main gear box.
The above defined powertrain may be controlled according to a first control strategy such that when a gear shift of the overall gear ratio from the first input shaft to the output shaft is made involving a change of engagement of the double clutch arrangement from the second clutch, engaging the second power path, to the first clutch, engaging the first power path, the power connection between the second propulsion unit and the second power path is maintained.
According to a second control strategy, which may be used alone or together with the first mentioned control strategy, the powertrain may be controlled such that when a gear shift of the overall gear ratio is made by changing the double clutch engagement from the first clutch to the second clutch, the power connection between the second propulsion unit and the second power path is maintained provided that the desired gear of the main gear box associated with the second power path already is selected in order to shift to the desired overall gear ratio from the first input shaft to the output shaft.
According to a third control strategy, which may be used alone or together with both or either of the first and second mentioned control strategy, also relates to controlling the power train when a gear shift of the overall gear ratio is made by changing the double clutch engagement from the first clutch to the second clutch. In this case the power connection between the second propulsion unit and the second power path is interrupted if there is a need to change the main gear of the second power path in order to get the desired overall gear ratio from the first input shaft to the output shaft. The shift sequence is controlled such that the shift of the main gear in the second power path is performed before the change of the double clutch engagement from the first clutch to the second clutch is performed.
The control method may be performed on a powertrain in which the gear ratios of the main gears in the main gear box associated with the first and second power path are the same and the gear ratio for the first clutch of the double clutch is different from the gear ratio for the second clutch of the double clutch arrangement.
Further details and advantages of the invention will be obvious from the embodiments of the invention described in the following.